[Fix #49796] Prevent global cache options being overwritten

The reason of removing dup 5 years ago in 6da99b4 was to decrease memory allocations, so, it makes sense to only dup options when we know they will be overwritten.

activesupport/lib/active_support/cache.rb

@@ -1053,6 +1053,8 @@ def get_entry_value(entry, name, options)
         end
 
         def save_block_result_to_cache(name, options)
+          options = options.dup
+
           result = instrument(:generate, name, options) do
             yield(name, WriteOptions.new(options))
           end

activesupport/test/cache/behaviors/cache_store_behavior.rb

@@ -702,6 +702,17 @@ def test_cache_miss_instrumentation
     ActiveSupport::Notifications.unsubscribe "cache_read.active_support"
   end
 
+  def test_setting_options_in_fetch_block_does_not_change_cache_options
+    key = SecureRandom.uuid
+
+    assert_no_changes -> { @cache.options.dup } do
+      @cache.fetch(key) do |_key, options|
+        options.expires_in = 5.minutes
+        "bar"
+      end
+    end
+  end
+
   private
     def with_raise_on_invalid_cache_expiration_time(new_value, &block)
       old_value = ActiveSupport::Cache::Store.raise_on_invalid_cache_expiration_time